Bis-Pseudoindoxyls: A Compact Fluorophore with Red-Shifted Absorption and Fluorescence for Bioimaging Applications.

A new class of single benzene-based fluorophores, bis-pseudoindoxyls, was developed. The core scaffold 14CO25NH is constructed via a visible-light-induced radical cyclization. Subsequent N-alkylation produced pronounced bathochromic shifts. The optimized dye 14CO25Nallyl exhibited absorption and emission maxima at 621 and 687 nm, respectively, with a moderate quantum yield in CHCl3. These properties enable long-term live-cell imaging of lipid droplets in the red spectral region.